Generate Missing Data via Script

For generating a table of dates, take a look at the CALENDARAUTO() DAX function. This creates a Calculated Table across all the date range in your model.

Then you can add a column to that table that pulls the relevant Exchange Rate for the dates that have a value.

You could fill in the remaining Exchange Rate values by using the a DAX calculation like this:

FullExchangeRate =

CALCULATE(

   LASTNONBLANK(Query1[Exchange Rate], TRUE()) ,

   CALCULATETABLE( DATESYTD(Query1[Date]) ,

                   DATESBETWEEN(Query1[Date],

                                BLANK(),

                                LASTDATE(Query1[Date])

                  ) ,

                  ALL(Query1)) ,

   ALL(Query1)

)

There might be a more efficient way to do that, but it'll work!